Xdebug complains about /home/vagrant/.phpstorm_helpers not being mapped

I'm running phpstorm 2016.3.2 on windows.  My dev box is a vagrant php box built with puphpet and xdebug enabled.  My project is a drupal 8 site managed with composer.  I've set up a remote php interpreter for the vagrant and my run configuration is set to use the drupal autoloader and phpunit.xml.

Running the phpunit tests works just fine, debugging tests doesn't work though.

• When running my tests with "Debug" (instead of "Run"), the script doesn't stop at the breakpoints.
• When running my test with "Run" and the Listener for debug connections is toggled on, the script halts a few times complaining that /home/vagrant/.phpstorm_helpers or home/vagrant/- is not mapped (also don't know where I could map them too).  The script will eventually hit my breakpoints.

The run configuration also has PHP_IDE_CONFIG (serverName=...) and XDEBUG_CONFIG (idekey=...) environment variables set (removing them didn't help and the listener stopped working as well).

I've been looking around but can't find a lot of info on mapping phpstorm_helpers, so I presume it must be something specific.  Any suggestions ?